Open your ~.profile file as covered above and remove any Environment Variables. You can use what I pasted to fix your profile file.
Once done, please follow the steps I outlined in the post Tutorial I linked to.
sudo -i
thunar
Navigate to /etc/profile.d/ and open qt-style-override.sh and ensure it is set to qt5ct and not to gtk2
Then open qt-qpa-platform theme - set to qt5ct not to gtk2.
Now, navigate to (I Think, please let me know if this is the wrong location) /etc/X11/Xsession.d
Open the file 56zorin-os-lite-session
It should say export QT_QPA_PLATFORMTHEME=qt5ct and not gtk3 or gtk2
That should fix the error. You may need to log out and back in when finished.